Pickling inhibitor



252. cowosmous, 1 5

"I W Yatented FebTTZflQSS LAUIIIIHI 1,990,963 PICKLING INHIBITOR Jan Teppema, Cuyahoga Falls, Ohio, assignor to Wingfoot Corporation,

Wilmington, Del., a

corporation of Delaware No Drawing.

Application July I, 1934,

Serial No. 734,231

24 Claims.

This invention relates to the art of pickling ferrous metals. More particularly, it relates to the use as corrosion inhibitors in ferrous metal pickling baths of a new class of materials which have been found to be extremely effective in retarding the attack of pickling acids on the metal or metals being pickled, but at the same time not to impair to any substantial extent the action of the acid on scale and rust. The compounds to which the invention relates, while not such as to dissolve readily in all of the more common acids, have the advantage that, once having been dispersed in the manner hereinafter described, they remain in dispersion in the acids ordinarlly used for pickling and hence do not form a scum on the surface thereof.

It has been customary heretofore to remove scale and rust from the surface of iron, steel and other ferrous metals by pickling the metal in a dilute solution of sulphuric or hydrochloric acid, usually heated to a temperature of 70 degrees C., to accelerate dissolution of the iron oxides. One dimculty has been that the pickling acid, in addition to dissolving the iron oxides, at-

tacks the ferrous metal itself, liberating hydrogen gas, which on escaping to the atmosphere, carries some of the acid with it in the form of which is very disagreeable to persons "inthe vicinity. The solution of the ferrous metal in the pickling bath is also undesirable, both because of the loss of acid and because of the fact that the process of solution is not uniform, but localized, causing pitting of the surface.

This invention resides, among other things, in the discovery of a new class of compounds which inhibit the dissolution of the ferrous metal by the pickling acid, but which have very little or no retax-ding effect on the action of the pickling acid on scale and rust. The class of compounds in question are the reaction products of mercaptazoles, su l 1 as mercaptothiazoles and mercaptoxazoles, formaldehyde and an ammonium sulphide, such a's ammonium hydrogen sulphide, (NI-IiI-IS), and ammonium sulphide (NHnzS. The exact constitution of these reaction products is as yet not definitely known; consequently, they will be referred to herein as reaction products.

In the preparation of these reaction products 50 several variations of procedure are possible. Thus, formaldehyde and the desired ammonium sulphide may be first reacted and this reaction product reacted with ammonium sulphide may be reacted with the 5 niercaptazole and reaction product reacted the mercaptazole. Also, the

with formaldehyde. Another procedure is to first react the mercaptazole and formaldehyde and then treat this reaction product with the ammonium sulphide. A still further procedure is to read; all three reactants at once.

If a reaction product of formaldehyde and the desired ammonium sulphide is to be prepared first, it is obtained by simply reacting the two materials. Since the react.on is exothermic, it is generally preferable to react the materials in the cold. One method which has been found particularly suitable is that in which 1000 parts by weight of an approximately 40% aqueous solution of ammonium hydrogen sulphide, cooled with approximately 600 parts of ice, are mixed with 1620 parts by weight of an aqueous 37% formaldehyde solution. An exothermic reaction takes place with the separation of a white gummy mass which gradually resinifies. This material, after being permitted to stand for some time, is ground to a fine powder, washed with water, and dried. The reaction product may then be reacted with a mercaptazole as will be described hereinafter. It is to be understood that it is not necessary to first grind the reaction product, wash it and dry it before its further reaction with the mercaptazole.

In the above example, the formaldehyde and ammonium hydrogen sulphide are reacted in the proportion of five mols of aldehyde to two mols of the sulphide. Although its exact constitution is not known, this particular product has been referred to in the literature as ipgritalmeihylqne diag' ngdisulphide. The following equation has been suggested for its formation:

It will be understood that despite the fact that a name and formula have been assigned to this reaction product, there is doubt as to its constitution.

While the reaction products of penta methylene diamino disulphide and mercaptazoles have been found to be extremely effective pickling inhibitors, it is to be understood that formaldehyde and ammonium hydrogen sulphide may be reacted in substantially any other proportions. Likewise other amm gniunrsiflphidessuchas ammonium sulphide (11028, maybe employed in w g or in admixture with, thefamjmonium hydrogen sulphide. M

Example 1 Illustrative of the invention, 32 parts by weight of l-mercaptobenzothiazole, 32 parts of the penta methylene diamino disulphide described above and 150 grams of toluol are heated under reflux. At first a clear solution is obtained, but as the reaction proceeds the reaction product becomes insoluble. After heating under reflux for a period of four hours,theinsolublematerialisfiltered off and extracted with 3% aqueous ammonia at a temperature in the neighborhood of the boiling point in order to remove any unreacted l-mercaptobenzothiazole. It will be found that the re- 1.5 parts of unreacted l-mercaptobenzothiazole. The reaction product is a grayish white material which melts in the neighborhood of 193-195 degrees C. While the exact formula of this reaction product is not known, it has been suggested that the following equation represents the reaction:

Alternatively, the reaction product described in Example 1 may be prepared simply by fusing the "penta methylene diamino disulphide" and the l-mercaptobenzothiazole, thus eliminating solvents entirely. In such case 147 grams of the penta methylene diamino disulphide are heated to 120 degrees C. Gradually 152 grams of 1- mercaptobenzothiazole are added thereto. The mass becomes stiffer with the addition of the mercaptobenzcthiazole and the temperature is correspondingly raised to 170 degrees C. and finally to 195 degrees C. The reaction is most violent at approximately 180 degrees C. The product is extracted three times with 3% boiling ammonia to remove traces of unreacted mercaptobenzothiazole, whereupon 260 parts of reaction product remain.

Example 3 Further illustrative of the invention, 83.5 parts of l-mercaptobenzothiazole are added to 116 parts of an aqueous solution of approximately 44% ammonium hydrogen sulphide. of a 37% aqueous formaldehyde solution are added thereto slowly, meanwhile agitating the mass vigorously and keeping the temperature at approximately 25 degrees C. The mass is then allowed to stand for 16 hours after which it is heated in boiling water. At approximately degrees C. the prcduct is gummy, but on raising the temperature to boiling a white, hard product is formed. The product, after being extracted with boiling ammonia, melts in the neighborhood of 188-190 degrees C. and is obtained in a yield of parts.

Example 4 In another variation of the procedure of reacting a mercaptazole, formaldehyde and an ammonium sulphide, 132 parts of a 38.8% aqueous ammonium hydrogen sulphide solution, 50 parts of 25% aqueous ammonia, 83.5 parts of l-mercaptobenzothiazole and 200 parts of ice are admixed. To this mixture is added slowly, with stirring, 250 parts of a 37% aqueous formaldehyde solution. After all the formaldehyde is added, the temperature is raised to the boiling point. A white reaction product is obtained, which after grinding and washing with 3% boil- Lamas ing ammonia solution, is obtained in a yield of 114 parts, melting in the neighborhood of 181- 184 degrees C.

Example 5 C-S-CHzOH,

forms, and is filtered and washed with water. To the wet cake of the benzothiazyl methylene hydrin are added 522 parts of a 39.5% aqueous ammonium hydrogen sulphide solution, 1200 parts of ice and 660 parts of a 37% aqueous formaldehyde solution. The mass is allowed to stand for 12 hours, meanwhile being agitated, and is then boiled for a period of approximately one hour. A white reaction product, which after being cooled, ground and washed with 2000 parts of a 3% NaOH solution at 25 degrees 0., is obtained in a yield of 560 parts and melts in the neighborhood of 195-198 degrees C. 32 parts of unreacted l-mercaptobenzothiazole are recovered after washing with the NaOH solution.

It will be understood that the benzothiazyl methylene hydrin may be prepared by other methods, such as, for example, by suspending 1- mercaptobenzothiazole in alcohol and adding formaldehyde. The benzothiazyl methylene hydrin is very soluble in alcohol and can be obtained in a pure form by crystallization.

It will be noted that the products obtained in Examples 1 to 5, inclusive, have slightly different melting points although the reacting materials are the same. These differences are caused by small amounts of impurities which vary according to the method of preparation employed. By dissolving any of the products of Examples 1 to 5 in nitro benzene and in symmetrical glyceryldichlor-hydrin and crystallizing them, they can be obtained in a substantially pure state, melting at 223-224 degrees 0.

Example 6 reaction product employing ammomum sulphide (NI-I028, 168 parts of 1- mercaptobenzothiazole are added to 256 parts of a 36% aqueous solution of ammonium sulphide and 400 parts of ice. To this mixture 492 parts of a 37% aqueous formaldehyde solution are added slowly with agitation. The mixture is allowed to stand for approximately one hour at a temperature not above 25 degrees C. after which the mass is heated to degrees C. A cream colored reaction product forms which, after being freed from unreacted l-mercaptobenzothiazole by extraction with a 2% aqueous sodium hydroxide solution at 80 degrees C., is obtained in a yield of 243 grams. The reaction product melts at -122 degrees C.

252. COMPOSITIONS,

Example 7 The reaction product of 4-chlor l-mercaptobenzothiazole, formaldehyde and ammonium hydrogen sulphide may conveniently be prepared by adding 64 parts by weight of 4-chlor l-mercaptobenzothiazole to 200 parts of ice, 19 parts of 28% aqueous ammonia and 64 parts of 39.5% aqueous NHiSH solution. The mixture is agitated and 123 parts of 37% aqueous formaldehyde solution are added slowly thereto. The mass is heated to the boiling point for approximately 15 minutes, whereupon a white reaction product forms. This reaction product, after being extracted with 500 parts of 3% caustic soda solution at 25 degrees C and dried, is obtained in the form of a white powder melting at 211-213 degrees C.

While the l-mercaptobenzothiazoles have been described in detail herein, it is to be understood that any other mercaptazole may be employed in the practice of the invention, examples being chlor l-mercaptobenzothiazole, 4-nitro l-mercaptobenzothiazole, 5-nitro l-mercaptobenzothiazole, 4-ch1or 5-nitro l-mercaptobenzothiazole, B-phenyl l-mercaptobenzothiazole, 3-methyl 1- mercaptobenzothiazole, 5-ethoxy l-mercaptobenzothiazole, 5-methoxy l-mercaptobenzothiazole, l-mercapto benzoxazole, l-mercapto tolyl thiazoles, dimethyl l-mercaptobenzothiazoles, S-phenyl S-mercapto 1-2-4-thiodiazole, l-mercapto naphthothiazoles, 3-p-tolyl 5-rnercapto 1-2-4-thiodiazole and S-mercapto 1-3-4- thiodiazoles. Any of these mercaptazoles may be reacted with formaldehyde and an ammonium sulphide according to the different variations of procedure described in the preceding examples.

Illustrating the effectiveness of these new reaction products as pickling inhibitors, mention may be made of comparative tests on several pickling baths, each consisting of 800 cc. of a 6% aqueous solution of sulphuric acid heated to 180 degrees F. One bath contained no inhibitor, while the others each contained 0.059 grams of various reaction products of the invention. Thin sheets of clean, hot rolled steel 3" x 4" in area adapted for tin plating were weighed and then one was placed in each bath ror'ell minutes; the 't''fnperatfirebeing maintained at approximately 180 degrees F. After this period the samples were dried and reweighed. The loss in weight of the various sheets of steel is as follows:

Losls1 in weir: t in Inhibitor grams per sq. in.

Control (no inhibitor) 0. 04550 0.059 grams of the reaction product of Ex. 4 0. 00005 0.059 grams of the reaction product of Ex. 6 0. 00214 In the practice of this invention on a commercial scale, an acid solution containing sulphuric acid is prepared in the usual manner and tra feasible since there is little danger of overpickling.

Metals may be pickled in the improved pickling solutions containing the inhibitors of the class hereinabove described in many widely different manners. Thus the metal may, if desired, be completely immersed in the acid, being carried into and out of the solution by known automatic devices. Alternatively, the solution may be sprayed onto the surface of the metal and later washed off by a water spray. The concentration of the acid and the temperature of the solution may be varied as desired and the inhibitors may be added in either greater or less proportions than described in the examples above. Even proportions as low as 0.01% by weight of the inhibitor based on the amount of acid employed are effective. comparatively large proportions may be necessary in some cases to reduce the corrosion of the metal to a minimum.

Although hydrochloric acid and sulphuric acid are generally employed in pickling operations because of their low cost, any of the other nonoxidizing acids may be substituted therefor in whole or in part. For example, pickling solutions containing phosphoric or hydrofluoric acid are useful in many cases. The concentrations ordinarily employed in commercial use; namely, from six to twelve percent, will generally be preferred.

The reaction products to which the invention relates are, in general, light in color and soluble in concentrated sulphuric acid solutions. Consequently, when employing one of them in a pickling bath, it is generally desirable to first dissolve it in concentrated sulphuric acid and then dilute the solution to the desired concentration or add such solution to the desired bath. This procedure, however, is not necessary in practicing the invention, colloidal dispersions being very effective in many cases. In other cases it is not necessary that the dispersion be colloidal, but it is, of course, generally desirable that the inhibitor be dispersed as well as possible throughout the pickling bath.

The property of being effectively dispersed in the pickling bath either by colloidal dispersion or by solution makes the reaction products of this invention particularly valuable since it permits the employment of relatively large proportions of the inhibitor without the attendant danger of a layer of scum or dirt being formed on the surface of the pickling bath, which contaminates the freshly pickled metal as it is withdrawn from the pickling solution. The use of a clean acid solution is, of course, desirable in any case but is particularly important where the washing tank is not near the pickling bath. By virtue of these and other advantages, ferrous metals pickled according to the teachings of the present invention are given a superior finish, thus making the invention highly valuable in operations such as tin plating, wherein it is necessary that the iron or steel to be plated be free of spots and stains. The inhibitors of this invention have been found particularly valuable with both low and high carbon steels, either normalized or not normalized. Other advantages are that pitting of the metal is almost completely eliminated, the consumption of acid and of metal is greatly reduced and embrittlement of the metal and formation of acid mist due to the evolution of hydrogen gas are largely prevented.

The reaction products of this invention may be employed as inhibitors by themselves or in diluted form with any of the well-known inhibitor diluents, such as kieselguhr, sulphite pulp and the like. They may of course be employed in the pickling of any metallic surface which lends itself to cleaning by the use of chemical agents in liquid form, but will preferably be employed with ferrous metals.

Although only the preferred embodiments of the invention have been described in detail, it will be apparent to those skilled in the art that the invention is not limited thereto, but on the other hand that various modifications may be made therein without departing from the spirit of the invention.

It is intended that the patent shall cover, by suitable expression in the appended claims, whatever features of patentable novelty reside in the invention.

What I claim is:

1. A pickling bath for metals containing a nonoxidizing mineral acid and a small amount of the reaction product of l-mercaptobenzothiazole and pentamethylene diamino disulphide.

2. A pickling bath for metals containing a nonoxidizing mineral acid and a small amount of the reaction product of a mercaptobenzothiazole and pentarnethylene diamino disulphide.

3. A pickling bath for metals containing a nonoxidizing mineral acid and a small amount of the reaction product of a l-mercapto aryl thiazole and penta methylene diamino disulphide.

4. A pickling bath for metals containing a nonoxidizing mineral acid and a small amount of the reaction product of a l-mercapto aryl azole and pentamethylene diamino disulphide.

5. A pickling bath for metals containing a nonoxidizing mineral acid and a small amount of the reaction product of a l-mercapto azole and pentamethylene diamino disulphide.

6. A pickling bath for iron or steel articles containing a non-oxidizing mineral acid and a small amount of a reaction product of a l-mercaptobenzothiazole, formaldehyde and ammonium hydrogen sulphide.

7. A pickling bath for iron or steel articles containing a non-oxidizing acid and a small amount of a reaction product of a l-mercaptobenzothiazole, formaldehyde and ammonium hydrogen sulphide, said materials having been reacted in the proportion of one mol of thiazole, five mols of aldehyde and two mols of ammonium sulphide.

8. A pickling bath for metals containing a nonoxidizing mineral acid and a small amount of the reaction product of a l-mercaptobenzothiazole, formaldehyde and an ammonium sulphide.

9. A pickling bath for metals containing a non-oxidizing mineral acid and a small amount of the reaction product of an aryl mercaptothiazole, formaldehyde and an ammonium sulphide.

10. A pickling bath for metals containing a non-oxidizing mineral acid and a small amount of the reaction product of an aryl mercaptazole, formaldehyde and an ammonium sulphide.

11. A pickling bath for metals containing a non-oxidizing mineral acid and a small amount of the reaction product of a mercaptazole, formaldehyde and an ammonium sulphide.

12. The process of cleaning ferrous metals which comprises treating said metals with a nonoxidizing mineral acid containing a small proportion of the reaction product of l-mercaptobenzothiazol'e and penta methylene diamino disulphide.

13. The process which comprises pickling iron or steel in sulphuric acid containing a small amount of the reaction product of l-mercaptobenzothiazole, formaldehyde and ammonium hydrogen sulphide.

14. The process which comprises pickling iron or steel in sulphuric acid containing a small amount of the reaction product of a l-mercapto aryl thiazole, formaldehyde and an ammonium sulphide, said materials being reacted in the proportion of one mol of mercaptothiazole, five mols of aldehyde and two mols of ammonium sulphide.

15. A pickling solution comprising a strong nonoxidizing acid and a small proportion of the reaction product of an ammonium salt of a lmercaptobenzothiazole and the reaction product of formaldehyde and ammonium hydrogen sulphide.

16. A pickling bath for metals containing a non-oxidizing mineral acid and a small amount of the reaction product of a mercaptazole, formaldehyde and ammonium sulphide.

17. A pickling bath for metals containing a non-oxidizing mineral acid and a small amount of the reaction product of a l-mercaptobenzothiazole, formaldehyde and ammonium sulphide.

18. The process which comprises pickling metals in a non-oxidizing acid containing a small amount of the reaction product of a mercaptazole, formaldehyde and an ammonium sulphide.

19. The process which comprises pickling ferrous metals in sulphuric acid containing a small amount of the reaction product of an aryl mercap'othiazole, formaldehyde and an ammonium sulphide.

20. The process which comprises pickling ferrous metals in sulphuric acid containing a small amount of the reaction product of a l-mercaptobenzothiazole, formaldehyde and ammonium sulphide.

21. The process which comprises pickling ferrous metals in sulphuric acid containing a small amount of the reaction product of an aryl mercaptothiazole, formaldehyde and ammonium sulphide.

22. The process which comprises pickling metals in a non-oxidizing acid containing a small amount of the reaction product of an aryl mercaptoxazole, formaldehyde and an ammonium sulphide.

23. A pickling bath for metals containing a non-oxidizing mineral acid and a small amount of the reaction product'of a l-mercaptobenzoxazole, formaldehyde and an ammonium sulphide having the formula (NH4)S--R, wherein R is hydrogen or ammonium. 24. The process which comprises pickling ferrous metals in sulphuric acid containing a small amount of the reaction product of an aryl mercaptothiazole, formaldehyde and an ammonium sulphide, having the formula (NH4)S-R, wherein R is hydrogen or ammonium.

JAN TEPPEMA. 

